Furnace



March 2, 1937. J. R. A. HoBsoN. JR 2,072,450

' FURNACE Filed May 13, 1932 2 Sheets-Sheet 1 INVENTOR ATTORNEY March 2,1937. J. R. A. HOBSON. JR 2,072,450

FURNACE Filed May 13, 1932 2 Sheets-Sheet 2 INVEENTOR W% /M W ATTORNEYPatented Mar. 2, 1937 TEE UNITED ATENT OFFICE FURNACE of PennsylvaniaApplication May 13, 1932, Serial No. 611,101

9 Claims.

This invention relates to furnaces, and more particularly to a furnaceadapted to burn finely divided, crushed or pulverized fuel having lowvolatile content such as anthracite fines or coke breeze, but is notlimited to the use of these materials. My improved furnace isparticularly adapted to fuels which have high ignition temperatures andwhich are diifieult to ignite and utilize in known types of furnaces, aswell as to fuels having ash with high fusion temperatures.

A specific object of the invention is the provision of an improvedsimple, compact and emcient furnace adapted to burn a fuel of relativelysmall size, the combustion preferably taking place With the fuel largelyin suspension in the combustion chamber. In accordance with theinvention, I provide means for heating the fuel prior to its injectioninto the burning zone and means whereby the fuel prior to and duringcombustion is under the influence of high radiant heat. Another featureof the invention resides in improved means for separating the finercombustible material in the fuel from the heavier particles and ash.Still another feature is a novel grate for burning out substantially allof the combustible from the ash and for removing the ash and clinkerfrom the furnace. The two last-mentioned features preferably includenovel means for supplying air through the grate and also thereabove, andfor controlling the amount of air supplied.

Through my invention the extent to which fuel is fed, combustion iscarried on, and ash is removed, can readily be controlled in accordancewith requirements, all without sacrifice of effioiency.

Other objects of my invention are to provide a furnace in which lowvolatile, small sized fuel can be burned at high rates of combustion andin which the supplies of air and fuel can be regulated eitherindependently or simultaneously so as to produce highly efficientcombustion and flexibility of operation. Further objects and ad vantagesof my invention will become apparent as the description proceeds.

My invention can best be explained by a detailed description of onepreferred form thereof, reference being had to the accompanying drawingsin which:

Fig. 1 shows, partly diagrammatically, a cross section of one embodimentof my invention as applied to a horizontal water tube boiler.

Fig. 2 is a partly diagrammatic View in cross section on the line 22 ofFig. l.

The main body ill of the furnacewhere the combustion takes place isconfined Within the front walls *3 and 4, the combustion arch 3 and 5,the sloping hearth 2, the bridge wall 32 and the side walls I6 and I6(see Fig. 2). This space is closed off at the bottom as will be morefully described later. At the top it communicates with the first pass llof the boiler I8.

Suitable conveying means such as the screw conveyor l are provided tointroduce the fuel into the furnace.

The rear wall of the furnace comprises the 10 sloping hearth 2 which ispreferably set at an angle to the horizontal somewhat greater than theangle of repose of the fuel to be used, but small enough so that thefuel is enabled to remain on the hearth over desired periods of time. It15 consists of a solid, preferably smooth surface composed of highlyrefractory material such as carborundum tile, or similar materialcapable of withstanding the high temperatures obtained during theoperation of the furnace. 20

At the bottom of the sloping hearth 2 and forming a continuation oftheslope is a wind box I?) with its perforated face plate 6 atsubstantially the same angle as the sloping solid hearth 2. Face plate 6is provided with perforations or openings which provide communicationfrom the wind box l9 into the combustion chamber I3. Below thecombustion chamber I3 is located an air supply duct 1 offrusto-pyramidal shape having its smallest horizontal cross section atits top forming a 30 throat la between the main duct 1 and thecombustion chamber Hi. The main air supply duct is formed by front plateI, rear plate I, and side plates 1". A rotatable, cylindrical grate 8and its housing positioned below the main air supply duct i preventsfree fall of larger fuel or ash particles to the ash pit.

At the lower end of the plates I and 1" are plates II and II" preferablysubstantially in the form of a horizontal cylinder which is open at thetop and the bottom, and which conforms closely to and contains acylindrical rotating grate. Plate II is joined to plate I, and plate IIis joined to plate 1" by suitable connections so that both plates II andII" are easily removable for repairs or replacements. Furthermore, theconnection between plate "I" and plate H" is preferably of hingedcharacter, plate ll" being held in position by a removable brace 20 foreasy adjustment, assembly and disassembly.

The grate 8, the air supply duct 1, and the plates II and II areconfined within the closed air chamber l2 while the interior of thegrate is in direct communication with it through apertures 28. This airchamber l2 forms a sealed ash pit which is an enclosed compartmentsubstantially bounded by the extension of the side wall l6 of thefurnace, front wall 4" of the furnace, the floors 2| and 22, and therear wall 23. It is provided with a suitable airtight door 24 so as toallow access to the air chamber I2 for repairs and replacements of thevarious parts within this space. There is also shown provided in thisspace suitable means such as a screw conveyor 25 for removing the asheswhich will be deposited in chamber l2 upon rotation of the grate.

The grate 8 comprises substantially a hollow ribbed cylinder. Thiscylinder, as indicated, is provided with a number of openings 28 whichcommunicate from the interior to the exterior of the cylinder. Theseopenings are desirably of such size that the proper volume of air maypass therethrough, but not large enough to allow passage of substantialamounts of fuel. Each end of the cylinder is closed off by a flange 26(Figure 2), each of which forms a seal 2'! with the plates 1". Theprojections or ribs 40 on the grate 8, conforming to the plates II andH, form a suitable seal as will be seen from Figure 1. Connected to eachof the flanges 26 is a hollow trunnion 34 mounted in a bearing 29. Thesetrunnions provide means of delivering air under pressure to the interiorof grate cylinder 8. Connected to one of the trunnions is a worm gearassembly II) or other suitable means for transmitting power to rotatethe grate cylinder 8. This worm gear assembly is in turn driven by anysuitable motive power (not shown) which will provide means for suitablerotation of the cylindrical grate 8, preferably slowly and continuously,though possibly intermittently. The Worm gear shaft may be carriedthrough the front wall 4 of the furnace setting, so as to allow for thecontrol and adjustment of rotation from a convenient point outside ofthe air chamber l2.

The fan 9, operated by the motor 30, furnishes air for combustionthrough the ducts l4 and I5. Duct l5, controlled by valve 33, deliversair under suitable pressure from the fan 9- to the wind box l9. Duct l4,controlled by valve 3|, is bifurcated to deliver air from the fan toeach of the hollow trunnions of the cylindrical grate 8 (Figure 2).

Suitable stufling box connections (not shown) may be provided betweenducts l4 and trunnions 34, if desired. The pressures in the duct t4, thetrunnion 34, the inside of the hollow grate 8, and the air chamber I 2,will be substantially the same since all of these parts are in directcommunication with one another. When the pressure in these parts isbuilt up sufficiently, the air will flow through openings 28 in thegrate and through the bed supported thereon. The pressure and quantityof air through the wind box I3 may be controlled independently of thepressure and quantity of air delivered to air chamber l2 by independentoperations of valves 3| and 33.

The movable brace 20 which holds the plate II" in position as indicated,is shown supported by the I beam 35 and the hanger 36. By means ofsuitable mechanism (such as the hand wheel 31, bevel gear 38 and theworm or screw and block 39) the loose end of plate ll may be moved inand out with respect to the rotating grate 8, from a convenientoperating position outside of the air chamber l2.

A feature of my invention is the construction of arch 3 and front wall4, and their relation to the sloping hearth and to the combustionchamber I3, so that they form surfaces for reflecting radiant heat backinto the combustion zone and onto the sloping hearth. I further preferthat front wall 4 and arch 3 be so positioned relative to the slopinghearth 2 that the opening between the nose 5 of the arch 3 and thesloping hearth 2 be somewhat restricted in cross-section relative to thegeneral cross-section of the combustion chamber l3. While forconvenience of construction a square corner is shown between flat walls3 and 4, it will be understood these walls may take other shapes andrelations not inconsistent with the preferred feature last mentioned.The arch 3 and wall 4 are desirably constructed of refractory materialsuch as high grade fire brick or tile.

The operation and certain advantages of my invention may be described asfollows:

Fuel is fed by means of the conveyor onto the solid sloping hearth 2,where it spreads over the face of the hearth and under the action ofgravity gradually slides down the slope provided by the hearth surface.During this travel down solid refractory hearth, the fuel is brought toa high temperature. Under load conditions the fuel reaches incandescencebefore striking the furnace face 6 of the wind box. This heating of thefuel in its progress down the hearth is accomplished largely through thereflection of heat from the front wall 4 of the furnace and from thesuspended arch 3. It is assisted. also by means of the restrictionbetween the nose 5 and the hearth 2, a condition which maintains andconlines the heat within the combustion space i3 so that reflection ontothe sloping hearth is obtained from the combustible particles insuspension. This preheating of the fuel serves two purposes. The firstof these is the substantial completion of desired endothermic reactionsprior to the introduction of the fuel into the main combustion zone,including the distillation of such volatile ingredients and moisture asmay be contained with the fuel. By this method a fuel of more uniformquality is supplied to the main combustion zone than would be the caseif the fuel contained its initial moisture and volatile content, asirrespective of the initial conditions of moisture and volatile contentthe proportion of these two in the fuel as it reaches the perforatedface plate 6 of the wind box is at a constant minimum value when usingmy invention. Furthermore, because substantially all of the volatilecontent has been eliminated, these endothermic I reactions do not limitthe temperature of the initial main combustion. The second feature whichI mention is the fact that the fuel before reaching the main combustionzone is heated to a high temperature, preferably near the ignitiontemperature. The necessity of adding sensible heat to the coal particlesin the combustion zone is, therefore, reduced to a minimum. These twofeatures are of extreme importance in my invention for the followingreason. With low volatile fuel a higher temperature is required toinitiate and maintain combustion than is nece sary with fuels of highvolatility. By the initial heating of the fuel, and incident substantialcompletion of the endothermic reactions, temperatures are maintainedhigher than the minimum required for the combustion of the fuels.

. On reaching the perforated face plate 6 of the wind box, the fuelmeets a number of high velocity blasts of air, advantageously at rightangles to the hearth, which force the finer particles of the fuel intosuspension and pro ide an intimate turbulent mixture of the fuel and theair. The finer fuel particles are thus carried in suspension into thecombustion chamber l3 and combustion is maintained preferably throughoutthis space. Inasmuch as the volume of the combustion chamber, as shown,increases toward the top, as the fuel and air stream are elevated, thevelocity or carrying capacity of the stream will decrease, thus allowingparticles of the incan descent fuel in the combustion stream to drop outand fall on the sloping hearth 2. There they mingle with the fresh fuelparticles delivered by the conveyor preferably in a substantiallycontinuous manner. The construction of my furnace, as shown, ispreferably such that the direction of the flow of gases through thefurnace facilitates the separation and movement of the particles towardthe sloping hearth rather than into the air jets. In this way, thoroughcommingling is obtained of the fresh fuel fed by the conveyor with thepartially combusted. fuel returned from the air stream. This furtherprovides for uniform and high temperatures in the initial combustionzone.

Depending on the size of comminuted fuel being used, the rate of fuelfeed and the pressure and volume of air being supplied through theperforated wind box face plate ii, a certain percentage of the coarserfuel particles or agglomerated particles of fuel, or ash, or both,passes over the perforated wind box face plate 6 and discharges into themain air supply stream entering the bottom of the combustion chamberthrough the throat la. Particles of sufficient size and weight toovercome the lifting effect of the main air stream through throat lafall into the main air supply duct 1 and onto the rotatable grate twhere any remaining combustible is consumed. Particlesnot sufficientlyheavy to overcome the lifting effect of the main air supply streamthrough the throat la are projected vertically upward into thecombustion space l3 commingling with the ignited finer fuel projectedfrom the perforated wind box face plate 6. Such fuel as passes theperforated wind box face plate 6 will, in general, comprise the largerparticles, and will be composed largely of agglomerated ash particleswhich consist of a number of small ash particles fused tog-ether withsuch small amounts of combustible as they may contain. A bed of theseparticles will be maintained within the main air supply duct 1 on top ofthe rotating grate and will be subject to a current of air which passesthrough the duct M, the trunnion 3t, and through the face openings 28 ofthe rotating grate 8 when these openings are in a position directlybelow the duct 1. This stream of air will be initially heated throughits contact with the rotating grate 8. This provides means of burru'ngout of such combustible as may be left in the bed which lies on top ofthe grate. As the stream of air passes through this bed, (thetemperature of which may be near the fusion point of the ash) it isheated to a high degree. On the other hand, the air entering the gratecools the same somewhat. 1 l

It will be understood from the preceding description that two streams ofair are preferably employed, one entering the combustion chamber itthrough the grate 8 and throat la (this stream being designated asprimary), and the other entering through the perforations in the faceplate ii of wind box i9 (this latter stream being termed secondary). Thesize of the holes in face plate 6 will be suitable for the purposesindicated and may vary somewhat depending on the size of fuel employed,as will be understood by those skilled in the art. As shown in Fig. 1,these streams preferably enter the combustion chamber adjacent the frontwall 4 of the furnace and advantageously converge a short distance abovethe throat 1a, with the result that desired turbulent flow of the gasesis increased. In other words, the construction is preferably such that asecondary air stream impinges upon a generally vertical primary streamclose to the wall 4, and intimately intermingles therewith, carrying hotparticles of coal generally in the path indicated.

By admitting the fuel at a point Ia, at the opposite side of the furnacefrom the air admission, and permitting the fuel to slide down the hearth2 a considerable distance before it reaches the entering air, and byemploying a wall 35 which converges toward the upper end of the hearth,the gas outlet port between the point for and the opposite portion ofthe wall 3-5 lies adjacent the portion of the hearth upon whichrelatively cold coal lies, so that the hot combustion gases areconcentrated upon and act to preheat the en tering coal by what may betermed a countercurrent heat exchange, the relatively cool air whichenters at the lower end of the hearth meeting fuel which has beenpreheated on the hearth. That is to say, the hot gases have to passsubstantially entirely over the hearth to reach the outlet port of thecombustion chamber, being admitted at the opposite side of the furnacefrom outlet port and being directed toward the hearth by wall 3-5.

A large portion of the air for combustion is thus highly heated prior toits introduction into the main combustion zone l3 and this greatlyassists in maintaining the high temperatures which are necessary for thecombustion of the low volatile fuel to which this invention isprincipally directed.

The velocity of the main air supply stream through the throat la effectsa classification of the material which has passed over the perforatedwind box face plate 6 into particles sufficiently light to be lifted bythe main air supply stream and blown upward into the combustion chamber!3 and particles heavy enough to fall through the main air supply streamand deposit on the rotatable grate 8. This is advantageous because itlimits the amount of combustible which must be burned out on therotatable grate 8.

As the particles of agglomerated clinker descend to the grate 8, theyare caught between the ribs on the grate 8. By the rotation of thegrate, the particles are carried in the pockets formed by the ribs andthe plate ii" and are finally discharged into the ash pit l2. From therethey may be removed by any suitable means such as the screw conveyor 25.The projecting rib of the rotating grate 8 entering the Zone of the ductI, has an upward movement which tends to loosen the bed of materiallying above the grate. The projecting rib of the rotating grate 3leaving the zone of the duct 1, exerts in combination with element II" ashearing action on the particles thus tending to break up any largeaccumulations which may lodge in the bed next to plate 1'. This providesa positive action for the removal of clinker. By the action of thepockets rotating within the plate I I", a substantially definitequantity of ash and clinker is removed at each revolution of therotating grate t. Thus, by proper regulation of the speed of therotating grate, a positive control of the height of material on thegrate is maintained. The rate of ash production will be governedsubstantially by two factors, the rate of fuel feed and the quantity ofash contained ina unit of fuel. The speed of the grate is in turncoordinated with these two factors. Since, prior to the dumping of theash, a bed containing this material may be maintained over the rotatinggrate at any reasonable height desired, the quantity of combustible inthe ash discharge from the furnace can be finally reduced to a minimum.The maintenance of such a bed over the grate is especially desirablewith fuel containing ash of high fusion point as without such a bedgreat difiiculty is encountered in securing an ash which is reasonablyfree from unburned combustible.

My invention provides an easy and economical Way of controlling thiscondition and further, it provides means of furnishing a large amount ofhighly preheated air to the combustion zone without the use of expensivepreheating equipment. 4

Under certain conditions of load, clinkers might be produced and beimperfectly comminuted by the action of the ribs against the fixedplates. Should this occur, plate H" may be moved by operation of thehand wheel 31. In this way, any undue pressure may be relieved byincreasing the space at the point of shear. This is necessary only onthe side towards which the ash rotates as indicated on the drawings.

Great flexibility of operation is readily available with my invention.That is to say, the furnace may be rapidly converted from a conditionWhere it is banked tov one of maximum heat generation per unit of time,by simple changes in the rates of feed of air and fuel, and possibly ofrotation of the grate. The furnace may be banked by simply reducing orstopping the feed of fuel, and reducing or preferably cutting off theflow of air through the wind box l9, though the speed of rotation of thegrate and the air stream therethrough may also be varied, if desired,for this same purpose. During banking, fuel will burn on the rotatinggrate 8 in a manner substantially the same as an ordinary hand fired pinhole hearth and will be confined to the limited space of duct 1,provided, as contemplated, that the holes in the wind box aresufficiently small to prevent any substantial amount of fuel frompassing therethrough. In this way, only a small amount of fuel will beconsumed during the banking period, and at the same time, sufficient hotcombustible will be available at all times to start operations underload without delay. In addition to providing for preheating of the fuelas it descends slowly along the inclined solid hearth 2, before it isbrought into contact with air blasts supplied through the perforatedwind box face plate 6 and the main air supply throat 1a and is blowninto suspension, I provide for a selective classification and stagecombustion of the fuel in first blowing out and projecting into thecombustion chamber l3, the finest portion of the fuel, by means of theair supplied through the perforated sloping face plate 6 and second inseparating coarser fuel and agglomerated ash or particles ofagglomerated ash containing some combustible, projecting the lighterparticles upward into the combustion chamber l3 for combustion anddropping the heavier particles to the rotatable grate for finalcombustion and discharge as ash. This stage combustion has distinctadvantages as it brings coarser fuel into contact with fresh air supplyin the main air stream before it is projected upward into the combustionzone of the burning finer coal projected from the perforated wind boxface plate 6.

By controlling the pressure in the wind box and the air pressurechamber, as well as the flow of fuel and the speed of the rotatinggrate, the operations of the furnace can easily be adjusted to conformto the load and to give high efficiency at all loads.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described, or portions thereof, but it is recognizedthat various modifications are possible Within the scope of theinvention claimed.

What I claim is:

l. A furnace adapted to burn comminuted fuel, said furnace includingwalls forming a combustion chamber, a solid hearth therein sloping at anangle to the horizontal slightly greater than the angle of repose offuel used, means for supplying fuel to the hearth adjacent the upper endthereof, means adjacent the lower end thereof for receiving fueltherefrom and for projecting part of the fuel into suspension in saidcombustion chamber, means adjacent to and below said last mentionedmeans for receiving fuel overflowing said last mentioned means andprojecting it upward and into suspension in said combustion chamber andmeans for collecting and discharging residues from the bottom of saidcombustion chamber.

2. A furnace adapted to burn comminuted fuel comprising walls forming acombustion chamber, a solid hearth therein sloping at an angle to thehorizontal slightly greater than the angle of repose of the fuel used,means for supplying fuel to the hearth adjacent the top thereof, asloping perforated plate adjacent to the lower end thereof and adaptedto receive fuel therefrom, means for supplying air under pressurethrough said perforated plate, a substantially vertical air supply ductadjacent the lower end of said perforated plate and positioned toreceive fuel therefrom, a grate below said air duct and means forsupplying air under pressure through said grate and said air duct forprojecting fuel into suspension in said combustion chamber.

3. A furnace according to claim 2 in which the grate is a hollow,rotatable grate.

4. A furnace according to claim 2 in which the perforated plate isdisposed at an angle adapted to direct air discharged therefrom towardand into the stream discharged from the air supply duct.

5. The method of burning comminuted fuel which comprises, preheating thefuel supported out of suspension in a combustion chamber; blowing astream of the finer size particles of the preheated fuel into suspensionby an air blast and burning them, and then flowing the coarser sizeparticles of preheated fuel into a second air blast and blowing a streamof said coarser fuel particles into suspension by said second air blastand burning them in the combustion chamber; separating heavy residuefrom lighter fuel in the second air blast and withdrawing the heavyresidues from the furnace.

6. The method of burning comminuted fuel according to claim 5 in whichthe burning stream of finer size fuel particles impinges on the streamof coarser size fuel particles.

'7. The method of burning comminuted fuel according to claim 5 in whichincompletely burned particles of the suspended fuel are dropped out andcommingled with the fuel being preheated and are again subjected to theaction of the two air blasts.

8. A furnace adapted to burn comminuted fuel, said furnace includingwalls forming a combustion chamber, a solid hearth therein sloping at anangle to the horizontal slightly greater than the angle of repose offuel used, means for supplying fuel to the hearth adjacent the upper endthereof, means adjacent the lower end thereof for receiving fueltherefrom and for projecting part of the fuel into suspension in saidcombustion chamber, means adjacent to and below said last mentionedmeans for receiving fuel overflowing said last mentioned means andprojecting it upward and into suspension in said combustion chamber,means adjacent to the upper end of said hearth and to said fuelsupplying means for venting products of combustion from said chamber,and

means for collecting and discharging residues from the bottom of saidcombustion chamber.

9. A furnace adapted to burn finely divided fuel comprising wallsforming a combustion chamber having a gas outlet at its top, astationary hearth therein sloping at an angle to the horizontal slightlygreater than the angle of repose of the fuel to be used, means forsupplying fuel to the hearth adjacent the top thereof, means forming asubstantially vertical air supply duct adjacent the lower end thereof, agrate below said hearth and adjacent low-er portion of said air duct anda perforated wind box between said hearth and said air duct for blowingfuel into suspension.

JOSEPH REID ANDERSON HOBSON. JR.

